The invention generally relates to hermetic compressors of the scroll type having a scroll mechanism which receives refrigerant at a suction pressure, compresses the received refrigerant, and discharges the compressed refrigerant at an elevated discharge pressure. Such scroll compressors are typically used in refrigeration, air conditioning and other such systems. The typical scroll mechanism includes an orbiting scroll member and a fixed scroll member, but may in an alternative form comprise co-rotating scroll members. Wraps are provided on each of the scroll members and face and intermesh with each other in an orbiting fashion so as to form pockets of compression during compressor operation.
Scroll compressors take various forms, such as high-side type compressors, wherein the internal volume of the compressor housing is primarily at discharge pressure, and low-side type compressors, wherein the internal volume is primarily at suction pressure. Efficiency in scroll mechanisms is primarily dependent upon maintaining pockets of compressed refrigerant gas during the compression cycle through to discharge with minimal leakage while consuming the least amount of energy to do so. Accordingly, it is extremely important to maintain the scroll set in a tight sealed relationship during compressor operation by maintaining the scroll set both radially and axially compliant. Typically, when the head pressure becomes extremely high the centrifugal forces that act to keep the scroll set radially compliant are overwhelmed and radial separation occurs. When the head pressure is very low axial separation may occur.
During compressor operation, pockets of compressed gas within the scroll set act upon the wraps so as to urge them axially apart. Separation of the scroll members results in leakage and inefficient compressor operation. Preventing scroll member separation is not simply a matter of applying a pressure on the back surface of the orbiting scroll which is sufficient to maintain contact of the tips of the scroll wraps with the inside face surfaces of the scroll members. Excessive wear on the tips of the scroll wraps occurs when excessive force is applied to the back of the orbiting scroll. The compressor must operate over a wide range of operating extremes which are somewhat dependent on the refrigerant system load connected to the compressor. At the high end of the compressor's operating range pressures are at their highest and, especially in a high-side design, the axial forces become greater and greater and the radial compliance force becomes less and less until leakage occurs due to the failure to maintain radial compliance. At the low end of the operating range the axial forces become less and less until they are insufficient to keep the scroll set tightly engaged and leakage occurs due to the failure to maintain axial compliance.
The pressure exerted against the back of the orbiting scroll member must be great enough to maintain tip to surface contact, while being not so great so as to cause excessive wear and power consumption and further operating inefficiencies. Some compressors have been arranged so that fluid at discharge pressure is applied at a portion of the orbiting scroll member and fluid at suction pressure are applied at a second portion of the orbiting scroll member. Other attempts have been made to apply fluid at a varying, intermediate pressure, alone or in conjunction with fluid at discharge and/or suction pressures, against the back of the orbiting scroll so as to expand the operating range of the compressor.
U.S. Pat. No. 4,475,874 (Sato) discloses a scroll compressor arranged to introduce an intermediate pressure gas from pockets of compression formed in the scroll set during compressor operation into a housing chamber formed in a compressor mechanism housing. The intermediate pressure fluid, at some level between discharge and suction pressures, is applied against the back surface of the orbiting scroll member so as to provide an axial biasing force which urges the orbiting scroll member tightly against the fixed scroll member. The intermediate pressure fluid is introduced into the housing chamber via at least one aperture provided in the end plate of one of the two scroll members. This in effect introduces a controlled leak from the scroll set to the intermediate pressure housing chamber. One disadvantage to this design is that it relies solely upon the fluid at intermediate pressure to provide the necessary upwards axial biasing force, and utilizes a relatively large volume of such fluid which must be drawn from the pockets of compression. This reduces the efficiency of the compressor mechanism.
U.S. Pat. No. Re. 33,473 (Hazaki) discloses a high-side scroll compressor having an oil passage which extends the length of the crankshaft for communicating oil from the sump to an oil chamber defined by the rear surface of the hub portion of the orbiting scroll member and the upper surface of the crank portion of the shaft. The sump and the oil in the oil chamber are at discharge pressure. Seals are used to isolate an intermediate pressure chamber, defined by the crankshaft, the frame, and the back surface of the orbiting scroll member, from discharge and suction pressures. At least one passage is formed in the orbiting scroll plate to communicate partially compressed gas from pockets of compression formed in the scroll set to the intermediate pressure chamber. The intermediate pressure gas that fills the intermediate chamber during compressor operation acts upon the rear surface of the orbiting scroll so as to urge it toward the fixed scroll member. The pressure level of the intermediate pressure gas is somewhat dependent upon the pressure of the suction gas entering the scroll set.
U.S. Pat. No. 4,384,831 (Ikegawa et al.) and U.S. Pat. No. 4,350,479 (Tojo et al.) disclose a scroll compressor having a liquid supply source that delivers oil under pressure via passages formed in the fixed scroll to a plurality of liquid confining pockets formed about the periphery of the interface of the scroll set for applying a force opposite to a localized high axial urging force. The force effected by the liquid source is provided to negate any moment resulting from the localized high axial force exerted on the orbiting scroll member during compressor operation. An intermediate pressure gas is delivered to a chamber defined by the frame, the back surface of the orbiting scroll member and the crankshaft via a pressure reducing valve which is connected to discharge pressure gas.